1. Field of Invention
This invention relates to surveying an existing overhead crane runway system to determine its straightness, span and elevation.
2. Description of the Related Art
An exemplary overhead crane, with which exemplary embodiments of the described rail survey carriage, or survey unit, and rail survey data collection methods may be used, is shown in FIG. 13. As shown in FIG. 13, such a traveling overhead crane 1300 may span a distance between two crane rails 1302, each crane rail supported by a crane girder 1304, and each crane girder supported by a plurality of support columns 1306.
Overhead crane 1300 may contact each of crane rails 1302 with an end truck 1308. Each end truck may include two or more wheels 1316 that contact crane rail 1302. For example, each end truck 1308 shown in FIG. 13 includes four end truck wheels 1316. The leading/trailing ends of each end truck 1308 is terminated with a rail sweep 1314.
Overhead crane 1300 may further include a trolley 1318 that travels between the two respective end trucks1308 on a pair of bridge rails 1320, each bridge rail supported by a bridge girder 1319. Trolley 1318 may further include one or more hoisting mechanisms 1322, each supporting a load hook 1324 which may be raised and lowered by each of the respective hoisting mechanisms to raise and lower cargo. Use of hoisting mechanisms 1322 to raise and lower cargo, coupled with the ability of trolley 1318 to travel back and forth between the two respective end trucks 1308 on bridge rails 1320, coupled with the ability of overhead crane 1300, as a whole, to travel the length of crane rails 1302, allows crane operators to move cargo between any two locations on the loading dock between crane rails 1302. Operation of the crane may be controlled by a crane operator located in a control cab 1326.
Overhead cranes, as described above, are used in material handling factories and warehouses around the world to load and unload millions of tons of cargo daily and are crucial to the daily operations performed at each of these respective factories and warehouses. Due to the large scale of such overhead cranes and the heavy loads typically transported by the cranes, proper alignment of crane rails and crane wheels is crucial to their safe and efficient operation, and hence crucial to the daily operations of each business in which they are used.
Alignment standards for crane rails are outlined in the Crane Manufacturers Association of America's specification 70 and AISE technical report #13. Many types of rail surveys involve time-consuming methods that require the rail to be locked out (i.e., power to the hot rail turned off) and survey personnel to walk the length of the runway.
Although alignment of the crane rails is important, other factors, such as positioning of crane end truck wheels parallel to their respective crane rails and/or assuring that drive motor output provided to the respective end trucks is equivalent, are also important. Imbalances in motor output to the respective end trucks can cause crane skew even though the crane rails themselves are within tolerance guidelines. These imbalances result in wear on the rail and crane wheels, both of which are costly to repair. Hence, a safe method to quickly and accurately collect rail survey data and to find the root cause of misalignment problems would be very beneficial.
Previous methods of rail surveying have involved using piano wire for straightening sections of rail. This method, when used in conjunction with a tape measure to measure the span between crane rails, is not very accurate and is extremely time consuming. Another common method requires setting a transit on the rail while survey personnel walk the length of the rail, stopping at various points to take readings. Whereas this is a more accurate approach for determining the straightness of individual crane rails, determining the span between crane rails is still dependent on the use of a tape measure. For measurement of crane rail elevation, yet another instrument is required for set-up on the rail. With two exceptions, the prior art for rail surveying refers primarily to techniques for use on train tracks and elevation tracks which are not applicable for use with respect to overhead cranes.
One exception is found in U.S. Patent Application Publication No. U.S. 2005/0111012, filed Nov. 25, 2003 by Steven K. Waisanen and published May 26, 2005 (Waisanen), which describes a laser survey device, which uses a remotely operated laser to perform a runway survey.
The laser survey device described in Waisanen includes a stationary component, that includes a self-leveling laser, and a mobile component, that includes a screen and an image capture device. In operation, the stationary self-leveling laser emits a beam of laser light towards the screen of the mobile component as the mobile component travels along the length of a crane rail. As the mobile screen travels along the length of the crane rail, the location of impact of the laser light on the mobile screen changes depending on movement of the mobile screen within a plane perpendicular to the steady beam of laser light emitted by the stationary, self-leveling laser. The image capture device captures and transmits to a remote computer information related to the location of impact of the laser light on the mobile screen. The remote computer uses the received information to assess the alignment of the crane rail.
Although Waisanen, at paragraphs [0024]-[0025] and in claim 16, indicates that the device can be modified for operation on a variety of crane rail configurations, Waisanen does not provide any details related to such alternate embodiments. For example, the detailed description and drawings depict only a device suited for use with a bottom-running crane rail configuration.
U.S. Pat. No. 6,415,208, filed Feb. 28, 2000, by Romuald Pojda, and issued Jul. 2, 2002 (Pojda), describes a laser-based survey device that is very similar, in both design and operation, to the laser-based survey device described in Waisanen. However, the device described in Pojda is configured to collect alignment data for top-rail crane rail configuration.
Although the devices described in Waisanen and Pojda may be used to collect alignment information for a single crane rail, the systems suffer from serious deficiencies. For example, both systems rely on a complex combination of electronics and some device embodiments are self-propelled. Such complex devices, mounted in the often harsh operational environment of some facilities, are likely to fail, resulting in lost operational capability, a need for specialized repairs, and, possibly, down-time for the crane itself.
Further, the devices described in Waisanen or Pojda are not capable of providing crane operators with sufficient information to quickly and accurately identify the root cause of misalignment problems within an overhead crane system. For example, the devices described in Waisanen and Pojda are capable of providing rail alignment information only. Neither the Waisanen device nor the Pojda device is capable of providing information related to span alignment, or elevation. Further, neither device is capable of providing timely information related to crane skew which may be used to identify and correct imbalances in the drive motors so as to avoid operating conditions in which the crane end truck wheels are not positioned parallel to the crane rails, and thereby avoid stresses that may result in misalignment of the respective crane rails, and wear to the crane rail and end truck wheels, all of which are costly to repair.